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Condensed matter

Condensed matter

Neutron scattering: strategic necessity or expensive luxury?

01 Apr 1999

Neutron scattering is a powerful probe of the solid state that underpins many areas of condensed-matter science. Bob Cywinski argues for an urgent commitment to new neutron facilities and liberal access to existing facilities.

Uniquely useful

In 1994 the Nobel Prize for Physics was awarded to Cliff Shull and Bert Brockhouse for, in the words of the Nobel committee’s citation, showing “where atoms are” and “what atoms do”, respectively. Some 40 years ago Shull and Brockhouse developed and demonstrated a uniquely powerful and universally applicable non-destructive technique for probing the structures and dynamics of solids and liquids. Today the same technique underpins the whole of condensed-matter science, from physics to engineering, from chemistry to biology, and from materials science to the earth sciences. This remarkably ubiquitous tool is, of course, neutron scattering, and the award of the Nobel prize to Shull and Brockhouse provided an unequivocal but belated acknowledgement of the wide scientific and technological importance that neutron-beam research has assumed.

Over the last 40 years the available thermal-neutron fluxes have increased by three orders of magnitude, and the range of experimental neutron techniques and instrumentation has expanded enormously, allowing increasingly complex scientific and technological problems to be solved. In the last decade alone there has been tremendous progress in our understanding of the microscopic properties of polymers, proteins, plastics, zeolites, alloys, glasses, ionic conductors, liquid crystals, ceramics, surfactants, quantum fluids, magnets and superconductors arising directly, and often solely, from neutron-scattering studies. The high penetrating power of thermal neutrons has been exploited in studies of materials in complex environments at extreme temperatures and pressures, and in tomographic studies of internal strain fields in engine components and even in railway lines. More recently kinetic in situ studies of bulk-material processing under realistic conditions have become routine. The information provided by these neutron studies is crucial to the development and optimization of many structural and functional materials that contribute to our quality of life. The neutron-scattering community One measure of the success and increasing popularity of neutron scattering is the steady growth of an international multidisciplinary neutron-scattering community. The number of neutron-beam users in OECD countries has increased from some 4000 in 1994 to about 7000 today. According to a recent survey prepared by the European Neutron Scattering Association (ENSA) and published by the European Science Foundation (ESF), almost two-thirds of this community is based in Europe. Interestingly, the same ENSA survey indicates that more than half of all European neutron-beam users are chemists and materials scientists, while the majority use neutron scattering as only one component of much wider research programmes.

This dispels a common myth that neutron scattering is a specialist tool used mainly by physicists. Indeed, the ENSA survey reveals a vibrant and broad programme of research, in which European neutron scatterers are well served by no fewer than 13 neutron facilities. Two of these facilities – the high-flux research reactor at the Institut Laue Langevin (ILL) in Grenoble (the major partners in which are the UK, France and Germany) and the ISIS pulsed spallation neutron source at the Rutherford Appleton Laboratory in the UK – are by far the most intense neutron sources of their kind in the world. Together, the ILL and ISIS have allowed Europe to establish a clear world lead in neutron scattering, and hence enjoy a pre-eminent position in condensed-matter science. At first sight European neutron scattering thus appears to be enjoying a golden age. Sadly, this is not the case, and in many respects the prospects are bleak.

The impending neutron drought

The ENSA survey shows that the current demand for neutron beam time within Europe exceeds supply by almost a factor of two. It is generally considered that such an oversubscription engenders healthy competition and helps to maintain the high standard of European neutron science. However, a recent report written on behalf of the OECD Megascience Forum by Dieter Richter and Tasso Springer from the Institute for Solid-State Physics in Jülich, Germany, which presents a 20-year forward look at neutron-scattering facilities in OECD countries and Russia, indicates that at some time between 2010 and 2020 “the presently installed capacity of neutron sources for beam research will decrease to a level below one third that of today”.

This major shortfall in neutron supply is the widely discussed “neutron drought”, in which an oversubscription of at least one order of magnitude appears to be inevitable. The drought is a direct consequence of the rapidly expanding user base, the increasing demand for neutron beam time, and the dramatic fall in the number of neutron facilities. The US and Japan, however, are both planning third-generation neutron sources based on the pulsed spallation principle, and upgrading their existing facilities. Indeed, US’s ultra-high-intensity Spallation Neutron Source at Oak Ridge in Tennessee and Japan’s Hadron Facility are both scheduled to come on-line towards the end of the next decade. Europe, however, is lagging behind in the provision of such much-needed third-generation neutron sources. The detailed scientific case and feasibility study for a European Spallation Source (ESS) with a projected intensity some 30 times that of ISIS has only recently been completed (Physics World December 1997 pp27-32), as have plans for a proposed ISIS equivalent in Austria and a second target station for ISIS itself. Given that the gestation period for any new neutron project is at least ten years, the timing of the necessary political and financial decisions is therefore crucially important. As the Richter-Springer report emphasizes, some continuity in the supply of neutrons for condensed-matter research will be ensured only if decisions to launch these proposals as full-scale projects are taken now. Any reticence by governments or funding agencies to commit resources to a strategic third-generation European neutron source will undoubtedly undermine the long-term stability of neutron-beam research in Europe, eliminate our world lead in neutron science, and damage the European condensed-matter science, engineering and technology bases.

Access to existing neutron facilities

If we accept that neutron scattering has a strategic role to play in European condensed-matter research, it is essential that we ensure free access to existing neutron facilities while optimizing the use of available beam time. Historically, these twin aims have been achieved, at least at the major European facilities, via a stringent peer-review process. Each proposed experiment (generally for three to four days of beam time) is evaluated individually for originality, feasibility, timeliness and impact by international panels who are expert in both neutron scattering and the appropriate scientific disciplines. This system, which has evolved over three decades, is both effective and fair.

However, a radically new system of access has recently been devised by the UK’s Engineering and Physical Sciences Research Council (EPSRC) and implemented at ISIS, in the face of vociferous opposition from neutron-beam users. Now all but 10% of ISIS beam time is evaluated and allocated not through direct access on an experiment-by-experiment basis, but as “tickets” within an extended research programme that typically lasts for three years. It is clear, even from these early days of operation, that the new ticket system is destined to erode and narrow the UK user base by all but excluding the many scientists who need to use neutron beams only occasionally. It limits the flexibility and responsive character of neutron-beam research – features that have proved particular strengths in recent years – by tying up a large proportion of ISIS beam time for extended periods. Moreover, the quality of the neutron-scattering experiments will be affected: neutron measurements predicted three years in advance may well not be topical, relevant or necessary by the time they are finally scheduled. Peer review of these extended grant proposals is also fraught with problems. Requests for long periods of neutron beam time may now be assessed by only two or three referees who have little knowledge of neutron methods: as long as the underlying scientific case looks good, the beam time will be allocated. In addition, the notional cost of a ticket, valued at more than £9000 per day, includes additional expenses, such as infrastructural, staffing and overhead costs that would not normally be met by the EPSRC.

Research proposals seeking tickets for an average neutron programme therefore appear to be exceptionally expensive, with the tickets generally doubling or tripling the cost of otherwise modest research proposals. On the one hand, referees are unsure how to deal with such large requests for research funding. On the other hand, the absence of ring-fenced funds for ISIS allows resources that should be allocated to this major strategic facility to be bled away to more conventional university-based research programmes, which appear, because of the UK dual-funding system, to be much cheaper and hence more cost-effective.

Needless to say, the ticket system has little or no support within the UK neutron-scattering community. It is generally hoped that the ticket system will either be abolished entirely, or that a substantially greater percentage of ISIS beam time will revert to direct access. A further option might be for the EPSRC to cover only the infrastructural costs of ISIS, leaving scientists to bid for tickets priced at a level that reflects the cost of the neutron experiment itself (i.e. £2000-3000 per beam day). In any event, it is worrying to hear rumours that the same system is being viewed somewhat approvingly by other national funding agencies. European neutron scatterers beware!

Value for money?

Finally, there is a general misconception that neutron scattering is an intrinsically expensive technique. While it is true that the operation of an international neutron facility requires substantial funds, these funds are not excessive when considered against scientific output. A recent OECD survey of the scientific output of civil research in the “G7” countries places the UK well ahead of the field with an index of 17.2 research papers per million pounds of government spending. Interestingly, this figure is closely matched by the index evaluated for ILL and ISIS on the basis of statistics provided to me by these facilities. The cost-effectiveness of neutron-scattering research is therefore similar to that of UK civil research programmes on average, and is much greater than that of the national averages for other G7 countries.

I hope that the various research councils and their advisors in the UK will come to accept that the world-leading neutron sources at ISIS and ILL are a tremendous bonus rather than an expensive burden. The councils should be encouraged to make adequate financial provision for the running, maintenance and further development of these two flagship facilities, while also budgeting for a UK contribution to a third-generation European neutron source, such as the ESS. In the meantime, I also hope that the councils will recognize the strategic value of ISIS and ILL to the whole of the UK condensed-matter science, engineering and technology programmes, and therefore move to liberalize rather than inhibit access to these remarkable facilities.

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